Acoustical diaphragm and mounting means



Nov. 12, 1935. w. c. STENGER ACOUSTICAL DIAPHRAGM AND MOUNTING MEANS Filed June 12, 1933 2 Sheets-Sheet l [721/8 72Z 57 dzllebala' C. fii yez Nov. 12, 1935. w TEN ER 2,020,705

ACOUSTICAL DIAPHRAGM AND MOUNTING MEANS Filed June 12, 1953 2 Sheets-Sheet 2 I we:

Patented Nov. 12, 1935 UNITED STATES PATENT OFFICE MEAN Willebald C. Stenger, Chicago, Ill.

Application June 12, 1933, Serial No. 675.409

8 Claims.

This invention relates to sound producing diaphragms and is illustrated in connection with electromagnetically operated sound reproducers of the kind commonly used in radio receiving sets.

It is endeavored by means of the improved de-' sign to attain a diaphragm of light weight and having the required degree of rigidity with reference to its eiiective area, and which is bodily responsive throughout to high frequency vibrations or to low frequency vibrations and has free action up to the desired amplitude, except that the diaphragm is under constraint with reference only to vibrations of excessive amplitude, which constraint is provided by an inwardly drawing peripheral support for the diaphragm.

A further purpose of the invention is to provide improved central and peripheral supports for acoustical diaphragms. Another purpose of the invention is to provide an improved arrangement for centering the movable or voice coil with reference to the poles of electromagnetic sound producing constructions.

Other purposes of the invention are to provide improvements in the forms and proportions of elliptical, oval and conical diaphragms.

The objects of the invention are accomplished by means of constructions as illustrated in the drawings in which:-

Figure 1 is a face view of a dynamic speaker constructed according to this invention.

Fig. 2 is a view in longitudinal section as indicated by the line 2-2 of Fig. 1.

Fig. 3 is a view in transverse section as indicated by the line 3-3 of Fig. 1.

Fig. 4 is a face view of a diaphragm and its mounting means for the purpose of illustrating features of the invention applied to a cone type of speaker.

Fig. 5 is a plan view showing the further modification in the form of the diaphragm.

Fig. 6 is a view in longitudinal section taken on the line 6-8 of Fig. 5.

Fig. 7 is a view in transverse section as indicated by the line of Fig. 5.

Reference is made to applicants Patent No. 1,913,645 dated June 13, 1933, which is a description of diaphragms of the general type to which the present improvements are applicable.

The diaphragm is made of light strong fibrous material such as paper, preferably Japanese paper, known as Goyu, which is shaped and arched according to these specifications. Each diaphragm is composed of a plurality of arched surface areas which surface areas meet in ridges radial to the center of the diaphragm. These ridges need not be prominent but are strong enough to add rigidity and strength to the diaphragm without adding to its weight. Also the diaphragm is thicker near the center than at its periphery and the decrease in thickness is gradual from the center toward the outer edge, in for example, low altitude diaphragms at the ratio of seven near the center to five near the outer edge.

The diaphragms are also arched differently 1o lengthwise than crosswise.

The rim of the diaphragm is held under tension inwardly by means of an inner support which is connected with the rim of the diaphragm by a soft, flexible, pliable fabric head in ring form. This bridgelike inner support for the rim of the diaphragm may either be carried by a peripheral support or an extension of the center pole piece of the magnet. The fabric head is held tautly stretched like a drum-head to restrain 2 the diaphragm against transverse marginal vibration while permitting limited axial vibration.

The support for the center or inner edge of the diaphragm consists of a flexible and. pliable spider-shaped piece of material which is attached 25 to the diaphragm and attached also to a center extension of the pole of the magnet. The diaphragm carries the movable coil of the electromagnetic means for actuating the diaphragm. This movable coil is wound around a collar which is secured to the center of the diaphragm and is concentric with the means for connecting the diaphragm with the pole piece of the magnet.

By referring to the drawings, it may be seen that the elliptical form of the diaphragm I, illustrated by Figures 1, 2 and 3, is supported at its periphery by means of a spider-shaped frame 2 to which it is clamped between the rim 3 of the frame and the outer rim 4 of an inwardly extending bridgelike structure 5, preferably of sheet 40 aluminum.

A ring of fabric 6 extends from the inner rim 1 of bridge 5 outwardly to and between the rims 3 and 4 and the arched diaphragm has a flange at its rim which is cemented to the ring 6. In 45 the form shown in Figs. 2 and 3, there is an extra piece of fabric 8 cemented to the back of the flange of the diaphragm l and also clamped between the rings 3 and 4. This piece 8 may be of the same material as the part 6.

The diaphragm has a central round opening 9 where it is flanged inwardly, as indicated at I0. A collar H is cemented to the diaphragm at the flange 10 and this collar has wound on it the cylindrical moving coil l2 which serves 66 radial relation with the pole piece while to impart vibrations to the diaphragm according to fluctuations of current passing over the coil and which is reacted upon by the steady electromagnet flux passing between the pole pieces I3 and i of the magnet. The steady field is produced by the large stationary coil l5 wound around the core or pole piece 13.

he pole piece has a central extension which is drilled out and threaded to receive a screw 2?. This screw through a washer i8 clamps the pole piece an anchor means L? for the diaphragm. The anchor is in the form of a spider of flexible and pliable material and serves to hold 1e diaphragm and the coil carried thereby in a fixed permittlag T ting the diaphragm to move axially of piece.

It is designed to allow free motion of the diaphragm in one direction but to prevent displacement thereof laterally with reference to the pole piece and to assure proper centering of phragm. A suitable material for i9 is a plurality of alternate layers of Goyu paper and rubberized linen cemented together with a flexible cement.

With this arrangement, there is no difficulty in removing and replacing diaphragms as the centering thereof is certain.

The diaphragm is differently arched throughout different areas thereof as may be seen from Figure 3. The lines 26 and ii are arbitrary base lines for the arches represented by the curved lines 22 and 23. The two curves and 23 of the diaphragm 1 meet at a longitudinally extending ridge 24. This ridge makes the diaphragm more rigid than if the curves 22 and 23 met less acutely. In the form of diaphragm illustrated by Figures 1, 2 and 3 the longitudinal curvature increases gradually from the fiat peripheral flange 25 to the center.

The diaphragm varies in thickness; the maximum thickness being near the center, decreasing gradually towards the peripheral flange, for example in diaphragms used particularly for low altitude work, at the ratio of seven to five.

The shape and variations in thickness are the result of an eiiort to attain the freest possible motion of the diaphragm as a whole under the impressed impulses received at its center. It is essential to keep the diaphragm extremely light and responsive, consistent with the required strength and rigidity for preventing distortions or lag in movement of all portions of its area.

The curved surfaces of the various diaphragms are definitely arched according to their general contour and dimensions. In the former Stenger Patent No. 1,913,645 a chart and formula are given for the arching of the forms of diaphragms disclosed in that patent. In the present elliptical, oval and segmental conical diaphragms the arching comes close to 3 to 1 in one direction and 2 to l in another direction. For instance, lengthwise of the diaphragm shown by Figure 1, the length of the radius of the arch is twice the length of the radius of the arc. The radius of the arc is based upon the altitude of the diaphragm and its base. In the shorter crosswise dimensions of the diaphragm, it is arched by a radius which is three times the radius of the arc.

The same principles of construction are applied in the forms of diaphragms illustrated by Figures 4 and 5. Figure 4 relates to generally cone-shaped diaphragms but it is segmental in a sense in that the cone has radial corners and the areas between these corners are arched dif ferently in two directions and the curvature of the arches in an annular direction is of greater radius than if the diaphragm were truly conical. It is a shape involving characteristics of both pyramid and cone as indicated by the broken lines in Figs. 1 and 4. These broken lines represent the outer rim flange of the diaphragm and any section of the diaphragm taken parallel to the base is of similar form, except for the hereinbefore described flattening out of the transverse curvature toward the apex of the pyramidal fi ure. This arrangement again permits of lightness and rigidity, all of which adds to the responsiveness of the diaphragm and the brilliancy of the tone emitted thereby. The diaphragm is both centrally and peripherally supported from the center pole piece of the magnet. In the form shown in Figure 4, this pole piece carries the same anchoring means [9 as described in connection with Figures 1 and 2 and likewise carries the bridge or spider 25 which affords a peripheral support for the diaphragm through the connecting ring-shaped piece of fabric 26.

The oval form of diaphragm illustrated by Figures 5, 6 and 7 is substantially a combination of features of the elliptical form of diaphragm shown by Figure 1 and the more angular pyramidal form of acoustical diaphragms described in the Stenger Patent No. 1,913,645, of June 13, 1933. This oval diaphragm, like the others, is concavo-convex with arcuate surfaces extending both annularly and radially and the diaphragm has segmental areas each difiering from the other and is divided by radial stiffening ridges projecting either inwardly or outwardly from the surface of the diaphragm since these ridges are formed by individually arched segments, the curvature of which differs from the general oval surface of the entire diaphragm.

The dividing reinforcing ridges are indicated by the numeral 21. Between these ridges are segmental areas 28, 29, 30 and 3!, each diirering from the other in area as the coil supporting collar is not in the true center of the diaphragm. The acoustical center which is consistent with the best results for this form of diaphragm of low altitude is placed to one side of the geometrical center an amount which is found by dividing the square root of the area of the base by 112.5. The diaphragm may carry a heavy load without distortion and requires comparatively little power to drive it.

The arching of the different surfaces of the diaphragm in an annular direction is diagrammatically indicated by the lines 32 and 33 representing curvatures compared with the straight lines 34 and 35 representing the chords of the arcs of curvature of the diaphragm in the locality of such lines. The arching is progressive from the center of the diaphragm towards the periphery, being of greater curvature near the periphey.

In the operation of the diaphragm, the center support or means for anchoring the diaphragm to the pole piece of the magnet is pliable and non-resilient having the sole function of centering and of allowing the maximum freedom of the diaphragm for thrust motions. It is not a resilient restoring means for the diaphragm, as is commonly the case with bakelite or other resilient central anchoring means for diaphragms. The inwardly tensioning peripheral support for the diaphragm provided by the taut drumheadlike rings 6 and 26 permits free bodily motions of the diaphragm within decisive limitations which are offered by this support against vibrations hav- 16 ing amplitudes greater than that required for voice and musical sounds.

I claim:

1. A diaphragm of pyramidal form having sides of double curvature meeting in longitudinal ridges.

2. A diaphragm of pyramidal form having sides of double curvature meeting in radially disposed longitudinal ridges.

3. An acoustical diaphragm with a rim support which is placed inwardly from the rim of the diaphragm and is connected therewith by a ring of flexible, pliable material, said rim support being centrally mounted in fixed position and arranged to exert an inwardly directed pull on the margins of the diaphragm.

l. A curved diaphragm of the class described having a central non-resilient pliable supporting means, and a flexible rim support arranged to exert a flexing action on the diaphragm in a direction for increasing the radial curvature of the diaphragm during vibration.

5. A concavo-convex diaphragm substantially oval in outline and arched at its ends at a. ratio of 2 to 1 of its arc, determined by the altitude and base, and curved at its sides at a ratio of 3 to 1 to an arc determined by the altitude and base.

6. A concavo-convex diaphragm having its surface divided into segmental areas due to the curvature of such areas, and means for imparting movements to the diaphragm which means is placed to one side of the geometrical center of the diaphragm substantially an amount which is determined by dividing the square root of the base by 112.5.

7. In an electromagnetically operated sound producing apparatus, a supporting frame structure which is concavo-convex in form and has an elliptical outline, a magnet centrally mounted upon said frame structure, and an elliptical diaphragm having its rim attached to the elliptical rim of said frame structure.

8. An acoustical diaphragm of concave-convex form with a rim support comprising concentrically spaced fixed rings spaced respectively inward and outward from the outer rim of the diaphragm, and an annular head of flexible material stretched between said rings and fastened to the rim of the diaphragm to restrain lateral vibration thereof.

WILLEBALD C. STENGER. 

